Fiber-optic communication networks serve a key demand of the information age by providing high-speed data between network nodes. Fiber-optic communication networks include an aggregation of interconnected fiber-optic links. Simply stated, a fiber-optic link involves an optical signal source that emits information in the form of light into an optical fiber. Due to principles of internal reflection, the optical signal propagates through the optical fiber until it is eventually received into an optical signal receiver. If the fiber-optic link is bi-directional, information may be optically communicated in reverse typically using a separate optical fiber.
Fiber-optic links are used in a wide variety of applications, each requiring different lengths of fiber-optic links. For instance, relatively short fiber-optic links may be used to communicate information between a computer and its proximate peripherals, or between a local video source (such as a DVD or DVR) and a television. On the opposite extreme, however, fiber-optic links may extend hundreds or even thousands of kilometers when the information is to be communicated between two network nodes.
Long-haul and ultra-long-haul optics refers to the transmission of light signals over long fiber-optic links on the order of hundreds or thousands of kilometers. Typically, long-haul optics involves the transmission of optical signals on separate channels over a single optical fiber, each channel corresponding to a distinct wavelength of light using principles of Wavelength Division Multiplexing (WDM) or Dense WDM (DWDM).
Transmission of optical signals over such long distances using WDM or DWDM presents enormous technical challenges, especially at high bit rates in the gigabits per second per channel range. Significant time and resources may be required for any improvement in the art of high speed long-haul and ultra-long-haul optical communication. Each improvement can represent a significant advance since such improvements often lead to the more widespread availability of communications throughout the globe. Thus, such advances may potentially accelerate humankind's ability to collaborate, learn, do business, and the like, with geographical location becoming less and less relevant.
Repeaters that include optical amplifiers are often used in order to extend the reach of fiber-optic links. Such optical amplifiers may include, for instance, rare-Earth doped fibers and semiconductor-based optical pumps that power the rare-Earth doped fibers. The repeaters therefore have a supply of electrical power, and drop power to the optical pumps. The repeaters also have heat dissipation characteristics which allow the heat generated by the repeater to be dissipated to the ambient environment. Repeaters are often situated underwater perhaps on the ocean floor when, for instance, they are used for trans-oceanic fiber-optic links. Such repeaters are termed “submarine” optical repeaters. In submarine repeaters, the heat is to be dissipated to the surrounding ocean, which is typically just several degrees Celsius at the depths that most submarine repeaters operate at.
Repeaters typically include a housing, an insulating layer, and the amplifier assembly itself. The cable includes optical fiber pairs (each pair having an eastern fiber for communication in one direction, and a western fiber for communication in the opposite direction). The cable also has a conductor for delivery of electrical power.
The housing is typically composed of metal and is actually in contact with the ambient environment (sea water in the case of a submarine repeater). The insulating layer is typically a polymeric sleeve and acts to electrically insulate the amplifier assembly from the housing. The polymeric sleeve is typically in good intimate contact with the housing. In order to efficiently transfer heat from the amplifier assembly to the ambient environment outside of the housing, the amplifier assembly should also have intimate contact with the polymeric sleeve. This promotes heat transfer from the amplifier assembly, through the polymeric sleeve, through the housing, and into the ambient environment. Amplifiers are typically inserted into housings and then forced out mechanically against the polymeric sleeve to create the intimate contact required to promote good heat transfer.